This invention relates generally to a process for treating a brine system for an electrolytic cell. More specifically, it pertains to a process which controls the amount of excess carbonate added to the brine system to substantially remove by precipitation all of the calcium impurity in the brine as a calcium carbonate precipitated flocculant.
Typical methods of treating brine for electrolytic cell systems have employed feedback mechanisms which require frequent samplings of the brine based on conditions that are several hours old by the time the results are obtained. For example, where calcium carbonate is being measured in a settling tank, approximately 1-2 hours is necessary to obtain the settling of the calcium carbonate in order to obtain an accurate reading of the carbonate concentration. The carbonate concentration, as are most concentrations measured in a brine system, is determined by titration techniques. This approach does not give the concentration of the ionic species, in this instance carbonate, within the brine system at the time of sampling, but rather at the time 1-2 hours after the settling has occurred.
Additionally, prior systems employ carbonate addition which is controlled by a manually adjusted valve. Titrations are taken on a regular basis, such as every 2 hours, and the carbonate addition is adjusted as needed based on the titration results. There is no measurable basis in this type of a system, however, to determine how much to increase or decrease the carbonate addition. This frequently results in overshooting of the operating target. The amount of carbonate consumed during this type of a manually adjusted operation can be as much as 20% more than is necessary if the adjustment were optimally controlled. This approach suffers from a lack of knowledge of the current process conditions and requires costly, frequent sampling and analysis by operators. There is no rapid way to compensate for process upsets that periodically occur during operation.
These problems are solved in the use of the process of the present invention by providing a process to control the concentration of excess carbonate by the addition of sodium carbonate to electrolytic cell brine systems. The process can be automated.